Illumination systems, especially those utilized in endoscopic surgery, use a very high intensity lamp whose intensity cannot itself effectively be varied. Instead it is operated at full power, and means downstream from it are provided to reduce the quantum of light transmitted to the illuminated site. This avoids such complications as color change of the generated light which could be caused by operating the lamp at a lesser intensity, and some type of useful lamps simply cannot be operated successfully at a lesser intensity.
The reduction of transmitted light by lens systems using such expedients as irises is well-known and appropriate to other systems. However, such devices are not appropriate to fiber optic systems. This is because of the unique properties of fiber optic transmission.
A fiber receives a converging beam of light, and emits a beam rotationally faithful to its source. Accordingly, conventional masking devices tend to produce illuminating patterns whose brightness varies significantly across it. In some fields of work, this is tolerable. However, in the field of endoscopic surgery, for example, a small movement of the instrument could result in critical surgical area being too dark, or perhaps not illuminated at all.
This is not a neW problem, and there have been numerous efforts to provide a mechanical dimmer which will produce more even illumination across the illuminated field. Perhaps the most advanced such device known to the inventor herein is shown in Volpi U.S. Pat. No. 4,425,599. However, this and other previously known blocking means for dimming produce dimmer or dark sections, a phenomenon know as "ringing".
It is an object of this invention to provide a vane for dimming light which greatly reduces, even nearly eliminating, ringing, and having a substantial dynamic range of adjustment of light throughput, in this invention as great as 20:1.
It is another object of this invention to provide a vane which in various patterns of dimming, can provide effects ranging from exponentiaI attenuation to other mathematical relationships, such as linear.
It is another object of this invention to provide a dimmer in which the mechanism is rugged and simple, and once installed needs no care or attention other than keep it clean.